This invention pertains to the manufacture of liquid sampling cells of the type utilized in spectrophotometers. Such cells normally comprise a pair of windows transparent to the radiation to be employed, bonded to and separated by a metallic spacer which defines the sample space. For spectrophotometry in the infrared region, these windows are customarily made of salt crystals. Commonly used salts for this purpose are sodium chloride, potassium bromide, calcium fluoride, barium fluoride, thallium bromide iodide, cesium iodide, cesium bromide, silver chloride, and zinc selenide. Spacers are usually copper or lead and may vary from 0.015 to 1.0 mm in thickness.
The usual method of assembling a sample cell includes the steps of cleaning the crystal windows and the spacer. The spacer is then dipped in mercury and sandwiched between the windows. It is then allowed to sit under pressure two or three days.
The difficulty with the prior art procedure set forth above, is that the bond between the spacer and the crystals is not always adequate. In fact, the failure rate in producing cells by this technique is approximately 50%. Furthermore, the bond, even when technically adequate, often has a splotchy appearance.
For the foregoing reasons, it is a primary object of this invention to provide an improved method of manufacturing sealed cells for use in spectrophotometers. Other objects are: to provide such a method wherein improved sealing is obtained between the crystal windows and the spacer; wherein the failure rate in manufacture of the cells is substantially reduced; and wherein the appearance of the cells is improved. The manner in which the foregoing objects are achieved will be best understood by reference to the following description and appended claims.